Transmission system



April 29, 1947. slLVER 7 2,419,601

TRANSMISSION SYSTEM Filed April 27, 1945 5 Sheets-Sheet 1 TRANSMITTER RECEIVE? April 29, 1947,. M. SILVER 1 I 2,419,501

TRANSMISSION SYSTEM Filed April 2'7, 1943 5 Sheets-Sheet 2 a: #Hw

IN V EN TOR. MAmW/v s/z V61? A TTORNEY 29, 1947. M slLVER 2,419,601

TRANSMIS S ION SYSTEM Filed April 27, 1943 s sheets-sheet 5 gig/ :4.

l i l l ll v M CONT/POL V Patented Apr. 29, 1947 TRANSMISSION SYSTEM Martin Silver, New York, N. Y., assignor to Federal Telephone and Radio Corporation, East Newark, J a corporation of'Delaware Application April 27, 1943, Serial No. 484,700

3 Claims.

This-invention relates to transmission systems and more. particularly to transmission systems ofthe; type in which the. sets used for communication may be tuned to operate at different frequency bands.

In radio communication systems, it is often desirable to tune the communication sets to different frequencies of operation to avoid interference or the. like. This is ordinarily done in the. usual transmission-receiver arrangements by manually shifting the frequency as, for example, by push-button control means. Manual adjustment, however, suffers, from the disadvantage that allthe stations must know in advance what direction the shift is to take place in order to, stay tuned; together for intercommunication.

It is an. object of my invention to provide means for simultaneously shifting the communication frequency band at a plurality of communication sets.

It is a further object of my invention to provide a. special control signal which, will serve to vary the tuning of a plurality of communication sets in a predetermined cycle, to minimize danger of. interruption by interference.

It is a still further object of my invention to provide. a system applicable to, existing communication equipment which will serve to tune the equipment to different frequency bands.

According to a feature of my invention, each communication set is provided with means responsive. to a set of control signals to tune the sets simultaneously to different frequency bands. At a central point is provided a transmitter serving, to transmit control signals in a predetermined cycle so that tuning of the communication sets take place cyclically among the selected frequency bands. Periodically, a synchronizing signal is. transmitted to bring all sets into step should one or more of them be out of step. Preferably, the transmitter is provided with adjustable. controls so that should interference at any frequency become very acute, the period during which the sets are tuned to that frequency can be reduced or substantially eliminated.

A better understanding of my invention may be had from theparticular description thereof made with reference to the accompanying drawings, in which:

Fig. 1 illustrates a system in accordance with my invention, a control transmitter diagram thereof being shown in detail;

Fig. 2: is: a detail of a control key used with the control transmitter of Fig. 1;

Fig. 3i is a schematic circuit diagram of a communication set tuning control;

Fig. 4 is a schematic circuit. diagram or a modified communication set, tuningcontrol; and

Fig. 5 is a circuit diagram of av still further modification of the communication set tuning control.

In Fig. 1 is shown a system in which communication sets ii) and II, each preferably. consisting of transmitter and receiver equipment, are arranged for intercommunication. As indicated, this communication may take place over antennas 8 and 7. Sets 10, H are adapted to be tuned, to different selected communication frequencies by control signal energy from antenna 9, cou pled with control transmitter [2. Control transmitter I2, includes a tube [3", a tank circuit l4- and an impedance coil l5. A shown, the cathode of tube I3 is open at switch l9' o that no signals are being transmitted, The transmitter is designed to send out short control impulses 'to' operate tuning mechanism of communication sets I0, I l in a manner which will be described later.

In order to send out these impulses, switch i9- is closed periodically by a relay 20, the circuit of which is, completed by projecting contact closing elements 22, 23 arranged on a disc 2!. This disc together with, synchronizing disc 24' is rotated by a common motor 26 over a gearing mechanism 21. As disc 21 rotates, projections 22'serve toclose the circuit for relay 20, thus closing switch [9, and permitting pulses of energy to be transmitted from antenna 9 to sets l0 and H. 'The number of pulses transmitted during, a rotation of disc 2| depends upon the number of contact closing projectionsprqvided on the disc. It will thus be clear that transmitter [2 sends out a series of short, spaced impulses which serve to control the tuning of the communication sets.

However, since there may be quite a, number of sets communicating with one, another, the tuning circuits of some of the sets may failto operate for one or more of the pulses, thus throwing this set out of step, with the others. Before this set can be properly used for further com;- munication, it is necessary that it again be synchronized to operate with the remainin sets. For this purpose, synchronizing disc 24 is provided with a broad contact closing segment 25. This contact closing segment serves to energize relay 3%! closing a circuit at switch 2-9 for gas-, discharge tube 28. Gas-discharge tube 28 works into a time constant circuit 18, 3| producing a series of pulses closely spaced with one another and of a period dependent upon the time, constant, of the circuit. This pulse series is applied over resistance l'l' and inductance Hi6 to the control grid circuit of tube I3. At the same time a broadened contact projection 23 in disc 2i serves to retain relay 29 operative so that the oscillator is in condition to transmit the signals. The series of pulses applied to the grid of tube l3 serve to key this transmission and transmit a series of carrier frequency pulses corresponding to the pulses produced in the circuit of tube 28. This series of pulses serves to synchronize all of the stations in a manner to be described later in connection with the other figures.

It will be understood that each of the regularly spaced impulses transmitted under control of elements 22 serves to tune the communication sets sequentially to different frequencies among a plurality of bands. By thus tuning the receiver, it becomes more difiicult for an enemy to interfere with the communication by jamming the channels up on which transmission takes place. In order to jam the station the enemy would have to simultaneously switch his jamming transmitter to the various frequencies used in the transmitting circuit. Should, however, interference predominate in one of these bands, it is desirable that provisions be made to quickly tune the communication sets past this band so that interruption of communication would be minimized. In order to achieve this result, the control arrangement for transmitter i2 may be made adjustable, for example, in a manner shown in Fig. 2. In this figure, discs 21 and 24 are combined in the form of a single element 250.. On the upper surface of this element are mounted a plurality of switch control arms 22 held in place by a plate element 242). These arms are made adjustable between pairs of stop elements 32 on the surface of disc 24a so that the spacing between these arms may be adjusted at will. The broadened segment 23 used during the synchronizing period is fixed on the upper surface of this disc and on the lower surface of the disc is fixed a synchronizing element 25. These are arranged to coincide and engage contacts 23a and 25a substantially simultaneously so that the circuit of tube [3 will always be completed at the time tube 28 is energized. In Fig. 2 coils 2S and 30 are shown connected to current sources 20a and 30a. It will thus be clear that the control transmitter serves to send out a series of control impulses and periodically to send out a synchronizing signal.

The receiving control mechanism for the communication sets may be better understood by reference to Fig. 3 which shows one such system. In this figure, the communication set which may be a transmitter-receiver or a transmitter or a receiver is shown at 46 coupled to the normal receiving antenna 4!. In addition, there is provided a separate receiver arrangement 32 tunable to the quency of the control transmitter means of a tuned circuit did. The received impulses are detected in tube 42a and applied over a. coupling condenser :23 to a shaping tube M in the anode and screen grid circuit of which provided condensers 45 and .5 which serve together with the plate resistor 46a to shape the detected impulses to the desired form. The shaped pulses produced in tube 44 are taken oil across cathode resistor 47 and applied over cou pling condenser 38 to the delay line circuit consisting of resistances Bil, i and 52 and condensers 53 and 54. In addition, a time const circuit 56, 51 is provided to control the timing of application of these control impulses to the tuning control relays.

The impulses in coming over the delay line are applied to the grids of tubes 53, 59, and El. These tubes are of the gaseous discharge type. The delay line assures that potential is applied to the grids of these tubes in reverse order so that all the tubes of the system will always receive the control impulse. When the first impulse arrives only tube 58 can be triggered since this tube alone has a plate potential supply, the other tubes being open circuited at their plates by tubes 53, etc. This impulse will therefore cause tube 58 to ignite operating relay E8 and close a first switch 62. Closing of switch 52 serves to put condenser 53 across the set 48 tuning the set to a difierent frequency response band. At the same time, since tube 53 is now conductive, 13+ potential is applied to the anode of tube 53. Upon the arrival of the succeeding pulse, tube 59 will operate energizing a relay 69, closing switch 64 and putting condenser 65 in shunt with condenser 53 to tune the set to a still dilierent frequency. At the same time, tube EU is provided with a plate potential over ignited tubes 58, 59. Upon the arrival oi the next impulse, this tube will operate energizing relay 70, closing switch 66 to put condenser 6'. in parallel with the other condensers thus tuning the set to a still diilerent frequency. At the same time, plate supply is now iurnished to tube 6| in series through tubes 58, 59 and 59. Upon the arrival of the succeeding pulse, tube iii will be ignited energizing relay ii. Upon energization, the relay ll opens its contact 12 removing ground from tubes 58, 59 and 58 extinguishing these tubes. The circuit is thus returned to the normal inoperative condition and the transmitter-receiver is tuned to the initial frequency. The successive received pulses will cause the circuit arrangement to again repeat, the cycle just described so that the set will continuously be tuned to the various predetermined frequencies for which designed.

Should an enemy desire to interfere with the switching and send out a plurality of pulses, this would merely serve to speed up the switching of the communication sets from one frequency band to another and would not at all interrupt the communication. On the other hand, should the enemy attempt to interfere with the communications directly, it will be necessary to provide as many jamming frequencies as there are communication bands. It is, therefore, clear that this arrangement provides a certain amount of security from enemy interference.

Since communication sets may get out of step as explained above, it is necessary to provide means to assure that these sets may be brought back into step. This is accomplished by the transmission of the series of synchronizing pulses which are received at 42 detected and shaped in the same manner as of the control impulses. However, these impulses are influenced by time constant circuit 56, 51 so as to assure that all tubes of the system are energized simultaneously, thus returning all communication sets to the same initial transmitting condition. These synchronizing pulses are sent periodically so that should any receiver get out of step they will be brought into step at that time.

In the circuit arrangement of Fig. 3, relays such as 53, G9 and TE) once energized are maintained in energized condition until the complete cycle of control impulses has been received. In many cases, it may be desirable to have the relays released when the succeeding relay operates. However, at the same time, the tubes must be ants-b1 5 maintained ignited in "order that the plate supply for successive operation of the tubes may be provided. A system for accomplishing this result is shown in Fig. 4. In this figure the tubes are arranged to successively operate in precisely the same manner as the tubes of Fig. 3. However, I have shown an additional tuning controltube providing a series of live tubes instead of the'iourshown in Fig. 3. In this arrangement, once tube 58 has been operated plate supply is furnished to tube '59. Upon operation of tube 59, relay 69 serves to close a switch 84 putting a resistance 83 in parallel across the winding of relay 68 causing the relay to release. Resistance 83 serves to furnish plate voltage to maintain tube 58.operated. Upon energizing of tube 60 by the successive pulse, relay serves to shunt re sistance 85 across relay 69 by means of control of contact 86 so that this relay may drop. However, dropping of relay 69 removes the shunt resistor 83 from tube 58. This would cause relay 68 to reoperate. To prevent this, additional contact 81 is provided closed by energization of relay 10 to maintain resistance 83 in shunt across the winding of relay 68. Similarly, upon the energization of tube 8] a resistance 88 is shunted across relay l0 and at the same time switches 89, 90 and 91 serve to maintain the shunt connection of resistance 83, 85 and 88, across relays 68, 69 and "Ill, respectively. Upon operation of tube 6| normally closed switch 12 is opened causing release of all the relays so that the cycle may be repeated.

In Fig. 5 is provided a still further modification of the circuit arrangement at the receiver in which magnetic relays are used in the place of the gas-discharge control relays of Figs. 4 and 5. In this arrangement the first impulse applied from control receiver 42 serves to energize the main winding of a relay 58a. This relay operates closing at its upper contact 62a switch 52 shunting in condenser 63 across the communication set 40. At the same time, the energizing circuit for relay 58a is broken at the lower back contact 5% of 58a and a holding contact 580 for holding winding 96 is made at the lower front contact of relay 5311. This holding winding is sufficient to maintain switch 62 closed although it is insufficient to operate the relay. The closing of this holding contact winding also provides a ground for the successive relay 59a which ground may also be common ground for the hold,- ing winding 9'! of this relay. The succeeding pulse is thus applied over the back contact of relay 59a to the operating winding causing this relay to operate closing its upper contact 54 to adjust the tuning of the communication set. At the same time, the main winding 59a is open circuited at the back contact of relay 59a and the front contact of this relay serves to apply a ground to the next succeeding relay 60a. At the same time, holding winding 91 is energized to maintain switch 64 closed. Upon the arrival of the next pulse, relay 59a and holding winding 98 are similarly energized tuning the set to a still different frequency and the following pulse serves to operate 82a and holding winding 99 for a similar manner closing switch 80 and adding a condenser 95 to the tuning circuit thus tuning the set to a still different frequency. When the last pulse of the series arrives, it is applied over a switch contact arran ement to the main Winding of relay Bla. This relay, upon operating, opens switch 12, de-energizing holding windings 96, 91, 98 and 99 and returning the circuit to normal.

A time constant circuit 55, 51 isprovided to assure proper synchronizing in resp'onseto the synchronizing signals in a manner similar to that described in connection with Fig. 3.

It should be distinctly understood that the above embodiments are given merely by way of example and many modifications thereof may be readily apparent. For example, other types of tuning arrangements for the communication sets may be provided in place of the shunt condenser arrangement illustrated. I Furthermore, various types of impulse transmitters may be provided as desired for transmitting the control pulses. Likewise, contact commutators may be provided instead of the switch closing mechanism shown in connection with Figs. 1 and 2 and various other modifications will readily present themselves to one skilled in the art. It is, therefore, to be distinctly understood that the particular descriptions herein are not intended as a limitation on my invention as set forth in the objects of the invention and the appended claims.

I claim:

1. In a transmission system comprising a plurality of communication sets including transmitters and receivers tunable to different operating frequency bands for communication among said sets, the combination of means for sequentially tuning all said sets to successively different ones of said frequency bands comprising a central transmitter for transmitting a successive series of impulses at predetermined intervals, means at each set for receiving said transmitted impulses, and means responsive to said successively received impulses for tuning said sets in sequence to different of said operating frequency bands, said last named means comprising a plurality of gaseous discharge tubes corresponding in number to the number of said operating frequency bands,

said sets being tuned to a first of said frequency bands in the normal condition of said relays and said relays being connected for successive opera tion to tune said set to different of said bands, means responsive to successively received of said impulses for successively operating said relays, and means responsive to operation of each relay for conditioning the succeeding relay for operation, operation of the last of said relays serving to return said plurality of relays to their normal unoperated condition 2. In a transmission system comprising a plurality of communication sets including transmit ters and receivers tunable to different operating frequency bands for communication among said sets, the combination of means for sequentially tunin all said sets to successively different ones of said frequency bands comprising a central transmitter for transmitting a predetermined number of successive short impulses for tuning said sets to successively different ones of said frequency bands, and means for periodically transmittiw a relatively long impulse effect to insure synchronization of the tuning of all said communication sets, means at each set for receiving said transmitted impulses, and means responsive to said successively received impulses for tuning said sets in sequence to different ones of said operating frequency bands, said last-mentioned means including means responsive to said relatively long impulse effect for securing synchronization oi the tuning of said sets.

3. In a transmission system comprising a plurality of communication sets including transmitters and receivers tunable to different operating frequency bands for communication among said REFERENCES CITED The following references are of record in the file of this patent:

Number UNITED STATES PATENTS Name Date Burch et al Sept. 29, 1925 Chauveau Sept. 27, 1938 Michel Feb. 2, 1943 

